The mechanism of protein: protein association will be investigated using the interaction of calmodulin (CaM) and several of its target proteins as a model system. Three dimensional solution structures of CaM bound to various proteins will be determined: 1) the interaction between CaM and peptides corresponding to the two consecutive binding sites in myr4 (myosin I from rat); and 2) the interaction between apoCaM and the whole neuronal protein, neurogranin. The first project will include a thermodynamic investigation of myr4 recognition by CaM, to understand the unusual Ca2+-dependence of the interaction. The CaM:neurogranin structure would represent the first complex of CaM bound to an entire protein. Additional pressure dependence studies will be used to further elucidate the mechanism of this Ca2+-independent interaction, and will require the use of a novel high pressure NMR techniques developed by the Wand group. If time allows, additional thermodynamic studies are proposed addressing the determinants of target recognition using chimeric peptide substrates.